Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $91.32   7.792%   $98.4357   $98.44   $98.45   $98.40  
  Purchase #2 $163.75   8.128%   $177.0596   $177.06   $177.05   $177.10  
  Purchase #3 $8.39   11.356%   $9.3428   $9.34   $9.35   $9.30  
  Purchase #4 $77.27   12.210%   $86.7047   $86.70   $86.70   $86.70  
  Purchase #5 $41.45   4.479%   $43.3065   $43.31   $43.30   $43.30  
  Purchase #6 $203.81   6.791%   $217.6507   $217.65   $217.65   $217.70  
  Purchase #7 $169.28   12.515%   $190.4654   $190.47   $190.45   $190.50  
  7 purchase totals = $755.27       $822.9654   $822.97   $822.95   $823.00